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Exploring the anatomy and physiology of ageing part 6 - the eye and ear

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The sixth part in our series discusses age-related changes in the eye and ear, the sensory organs most profoundly affected by the ageing process

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Citation: Nigam,Y., Knight, J. (2008) Exploring the anatomy and physiology of ageing, part 6 - the Eye and Ear. Nursing Times; 104: 36, 22-23.

Authors: Yamni Nigam, PhD, MSc, BSc; John Knight, PhD, BSc; both lecturers in biomedical science, School of Health Science, Swansea University.

The ageing eye

Some age-related eye changes (Fig 1) may begin early in the third decade of life, with most anatomical and physiological processes following the typical gradual, linear decline with age.

Anatomical changes

The retro-orbital fat, which protects and cushions the eye, atrophies with age, leading to it receding into the eye socket (enopthalumus). Eyelid tissues can become lax and the levator muscle weaker, causing the eyelid to droop (ptosis), occluding some of the upper visual field.

Vision changes

Presbyopia happens to almost all individuals in their 40s and 50s. Reduced flexibility of the lens means it can no longer change shape to focus close objects (Montague et al, 2005). The distance from the eye at which print can be read increases from about 10cm at the age of 20 to about 100cm by the age of 70.

The pupil regulates the amount of light entering the eye. The size of the resting pupil decreases with age, which may reduce the amount of light admitted to the eye. Also, adapting to a change of illumination becomes more difficult. Dark adaptation depends on the regeneration of the photochemical pigment rhodopsin in the retinal photoreceptors, which becomes considerably delayed with age. Night vision problems commonly experienced by older people are attributed to this.

Tear production diminishes with age, causing dry eye, an uncomfortable sensation affecting more than 14% of people aged over 65. The cornea and conjunctiva become less sensitive so injuries may become less noticeable and therefore potentially more serious.

Cataracts

The lens becomes dense and yellow, affecting contrast sensitivity and colour perception and reducing the ability to distinguish between objects.

The increased density can reach a level where the lens proteins precipitate, scattering light entering the eye, a feature known as a cataract. Scattering of light causes glare, or a ‘halo’ effect when looking at bright lights, which can make it difficult to see in such conditions as driving at night. Senile cataracts typically occupy the central zone of the lens.

Posterior vitreous detachment (PVD)

With age, due to a structural change in the collagen fibrils (Bishop et al, 2004), the vitreous humour changes from a gel to a liquid, causing the vitreous mass to shrink and collapse, separating it from the retina. This is often seen as discrete opacities (floaters).

Cholesterol deposits may also cause general visual haziness.

Age-related macular degeneration (ARMD)

Photoreceptor cells die in the retina as we age, and the macula (fovea centralis), which provides highest resolution vision, also degenerates. The retinal pigment epithelium (RPE) fails to nourish retinal photoreceptors, which eventually die, causing the loss of central vision.

Two types of ARMD occur. Dry (atrophic) degeneration, which accounts for 90% of cases, is characterised by a gradual, progressive bilateral loss of vision. Wet (exudative) degeneration has a rapid onset characterised by severe and sudden loss of vision, caused by leaking blood vessels or serous fluid into the sub-retinal space.

Pale yellow-white elevated spots (drusen) appear on the retinal surface (Forrester et al, 2001), distorting vision and reducing visual acuity. Drusen increase steadily after the age of 60. ARMD accounts for half of all visual impairment in people aged over 75.

The ageing ear

The ear perceives sounds and maintains balance. The pinna (auricle) collects sound waves and directs them towards the eardrum, which vibrates in harmony. These vibrations are conducted to the auditory nerve, which carries the information to the brain. Balance sensory organs are located in the inner ear. Fluid and hair cells in the semi-circular canals govern the state of equilibrium. The entire auditory system undergoes changes with age.

Anatomical changes

The most common age-related changes to the external ear (pinna) include enlargement, external hair growth on the tragus and lower helix - mainly in males (Fig 2), increased scaliness, dryness and pigmentation spots. There is also a loss of elasticity in the ear canal, and ear canal collapse is common, leading to conductive hearing loss.

Anatomical changes to the middle ear include thinning and stiffening of the tympanic membrane, which also becomes less vascular with age (Weinstein, 2000).

The articular cartilage of the joints connecting the bones of the middle ear (ossicles) becomes calcified and thinner, particularly after the age of 70. Age-related atrophy of the musculature of the Eustachian tube may interfere with its opening during swallowing. Anatomically, age-related changes within the inner ear (primarily atrophy of support cells within the organ of Corti and degeneration of hair cells) have a significant impact on hearing.

Age-related hearing loss - presbycusis

Hearing is most acute and efficient at the age of 10 and gradually declines with age. This hearing loss is termed presbycusis. Physiologically, it is due to degeneration of the outer and inner hair cells of the organ of Corti. The outer hair cells are more vulnerable and most severe loss occurs in the basal region of the cochlea. This is associated with the significant loss of hearing at high frequencies which typifies presbycusis.

High frequencies aid the interpretation of speech, which therefore becomes difficult - especially when there are competing sounds such as background noise. Changes within the brain also slow the processing of auditory information. Other symptoms, such as tinnitus, are also common.

Cerumen accumulation

Cerumen (ear wax) in the external auditory canal, becomes drier with age (mainly due to decreased activity of the apocrine sweat glands). This increases likelihood of cerumen accumulation and ear canal obstruction, leading to conductive hearing loss.

Age-related balance impairment

Within the inner ear, the vestibular system consists of a labyrinth containing the semi-circular canals and their hair cells, and the otolith organ (utricle and saccule). These are key in maintaining balance. Changes in the vestibular apparatus include progressive loss of hair cells (Rauch et al, 2001) - after the age of 70 there is as much as a 40% reduction in the semi-circular canals. Other changes are fragmentation and degeneration of otoliths, particularly in the saccule. The number of vestibular nerve cells (Scarpa’s ganglion), diminishes from around 60 years. Such changes manifest as dizziness with falling a major health concern in older people.

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